This invention relates to electrostatographic reproducing apparatus and more particularly to simple apparatus for accurately positioning at least a portion of the copy sheet path which is defined by upper and lower frame portions.
In the electrostatographic reproducing apparatus commonly in use today, a photoconductive insulating member is typically charged to uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the usual document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developing powder referred to in the art as toner. Most development systems employ a developer material which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas in the photoconductive insulating area to form a powder image on the photoconductive area. This image may subsequently be transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure.
Typical of the electrostatographic reproducing apparatus commercially available today are the 3100 family of products including the 3400 and 3450 available from Xerox Corporation. In each of these machines the processor section of the reproducing apparatus is divided into at least two frame portions, an upper and a lower frame portion which each contain various sections of the processing equipment. Typically, the frame portions are hinged or pivoted about one end relative to one another. In these products, the paper path is generally horizontally oriented and is relatively straight through the machine. Furthermore the paper path is typically defined by elements in both of the frame portions, and in particular, rolls forming a pair of output drive nip rolls may be positioned in both the upper and the lower frame portions. These nip rolls must be precisely registered with respect to the paper path since, if they are not, it is possible for a sheet to strike the nip above or below the nip of the rolls forming a buckle upstream in the sheet which can further cause the formation of a buckle in the radiant fuser. When a buckle is formed in the radiant fuser, the copy paper frequently comes in contact with fuser elements resulting in the potential offset of toner material to the fuser thereby contaminating the fuser and subsequent copies. One way in which the registration of the paper path is insured is to precisely fix the position of the paper path by fixing the position of the transport mechanism prior to the position of the fuser and the position of the output roll from the fuser. The output roll in the lower frame portion is positively driven by a drive train which drives elements in both the upper and the lower frame portions. The idler roll in the upper frame is spring loaded to provide the necessary tension in the nip formed between the upper roll and the lower driven roll in the lower frame portion. In such an arrangement the drive train drives elements in both the upper frame portion and the lower frame portion thereby requiring more parts in the drive train, greatly increased assembly time, and much greater constraints in the design that the fixture can take. In addition, with a more complicated drive train, there are many more things that need to require servicing or that can malfunction. This arrangement is necessary since if the top roll were driven, a very complex driving mechanism would be required since it is very complicated and difficult to drive a spring loaded roll.